GAE Soft Memory Use

Question

I am new to Google App Engine, but trying to find the true source of how much soft memory my application is consuming.

I am running the F1 instance class (128MB Memory limit) in the standard environment and have not yet had a soft memory exceeded error.

The tools I am using to check memory are:

• Google App Engine Dashboard (Memory usage chart) - shows memory use gradually increasing over the past week from 250MB to over 1GB. Refer to first image below.
• Google App Engine Dashboard (Instance summary table) - shows the average Memory usage at 122MB. Refer to first image below.
• logging runtime.memory_usage() - shows a range between 120MB and 160MB throughout the day.
• Stackdriver Monitoring - shows memory mostly hovering around 150MB, but spiking as new instances are spawned. Refer to second image below.

Appreciate any guidance on which information source I should be using to determine the actual memory use of the application, and what Google would use to throw a soft memory error.

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App Engine Dashboard:

Stackdriver Monitoring:

Answer 1

App Engine won't throw an exception when you reach the soft limit. Instead, your instance will be gracefully restarted (stop accepting new requests, finish any existing requests, and shutdown).

In your first graph, the "250MB to over 1GB" is the aggregate memory usage over all your App Engine instances. You can see in the instance summary table that the average memory per instance is 122.3MB, so it's under the soft limit.

The Stackdriver graph is showing aggregate memory usage over a region. You can see that the spikes in memory correlate with multiple instances running simultaneously.